Having the advantages of mechanical strength (impact resistance), heat resistance and good electric properties, polycarbonate resins serve as engineering plastics and have many applications in various fields of, for example, electric and electronic appliances and automobile parts. Above all, colored polycarbonates are used, for example, for parts of electric and electronic appliances, parts of electrically-powered tools and parts of cameras. Glass fibers serving as an inorganic filler are added to such polycarbonate resins for improving the stiffness and dimensional stability of the resin articles, and they are known as glass fiber-reinforced polycarbonate resins.
Such glass fiber-reinforced polycarbonate resins are used for thin-wall moldings these days, and it is desired to increase the flowability of the resins. Lowering the molecular weight of polycarbonate is effective for increasing the resin flowability, which, however, greatly lowers the impact resistance of the resin articles.
To solve the problem, proposed are a composition that comprises a glass fiber-reinforced polycarbonate resin and an organosiloxane (Japanese Patent Publication No. 35929/1984, International Patent Publication No. 501860/1982) and a polycarbonate-polyorganosiloxane copolymer reinforced with glass fibers (Japanese Patent Laid-Open No. 173061/1990). The techniques proposed are to improve the balance of the resin flowability and the impact resistance of the resin articles, but are still unsatisfactory. Another problem with colored polycarbonate compositions is that the glossiness of their injection moldings is not good when ordinary polycarbonate is used in the compositions.
The first aspect of the invention has been made in consideration of the situation as above, and its object is to provide a colored polycarbonate resin composition of which the advantages are that its flowability is improved not detracting from the impact resistance of the resin moldings, and especially the glossiness of the injection moldings of the resin composition is extremely good.
As a rule, polycarbonate resins are self-extinguishable. However, in some fields of typically OA appliances, information and communication appliances, and other electric and electronic appliances for household use, required are polycarbonate resins of more improved flame retardancy. For these, various flame retardants are added to polycarbonate resins to meet the requirement.
For improving the flame retardancy of polycarbonate resins, halogen-containing flame retardants such as bisphenol A halides and halogenated polycarbonate oligomers have been used along with a flame retardation promoter such as antimony oxide, as their flame-retarding ability is good.
However, with the recent tendency toward safety living and environmental protection from discarded and incinerated wastes, the market requires flame retardation with non-halogen flame retardants. As non-halogen flame retardants, phosphorus-containing organic flame retardants, especially organic phosphate compounds may be added to polycarbonate resin compositions, for which various methods have been proposed. Such flame retardants, organic phosphate compounds serve also as a plasticizer, and polycarbonate resin compositions containing them exhibit excellent flame retardancy.
However, in order to make polycarbonate resins have good flame retardancy by adding thereto a phosphate compound, a relatively large amount of the compound must be added to the resins. In general, polycarbonate resins require relatively high molding temperatures, and their melt viscosity is high. Therefore, for molding them into thin-walled and large-sized moldings, the molding temperature will have to be higher. For these reasons, phosphate compounds often cause some problems when added to such polycarbonate resins, though their flame-retarding ability is good. For example, phosphate compounds often corrode molds used for molding resins containing them, and generate gas to have some unfavorable influences on the working environments and even on the appearance of the moldings. Another problem with phosphate compounds is that, when the moldings containing them are left under heat or in high-temperature and high-humidity conditions, the compounds lower the impact strength of the moldings and yellow the moldings. In addition, polycarbonate resin compositions containing phosphate compounds are not stable under heat, and therefore do not meet the recent requirement for recycling resin products. This is still another problem with phosphate compounds.
Apart from the above, proposed is another technique of adding silicone compounds to polycarbonate resins to make the resins have flame retardancy. In this, silicone compounds added to the resins do not give toxic gas when fired. For example, (1) Japanese Patent Laid-Open No. 139964/1998 discloses a flame retardant that comprises a silicone resin having a specific structure and a specific molecular weight.
(2) Japanese Patent Laid-Open Nos. 45160/1976, 318069/1989, 306265/1994, 12868/1996, 295796/1996, and Japanese Patent Publication No. 48947/1991 disclose silicone-containing, flame-retardant polycarbonate resin compositions.
The flame retardancy level of the products in (1) is high in some degree, but the impact resistance thereof is often low. The technology of (2) differs from that of (1) in that the silicones used in (2) do not act as a flame retardant by themselves, but are for improving the dropping resistance of resins, and some examples of silicones for that purpose are mentioned. Anyhow, in (2), the resins indispensably require an additional flame retardant of, for example, phosphate compounds or metal salts of Group 2 of the Periodic Table. Another problem with the flame-retardant polycarbonate resin compositions in (2) is that the flame retardant added thereto worsens the moldability and even the physical properties of the resin compositions and their moldings.
Also known is a flame-retardant polycarbonate resin composition that comprises a polycarbonate-polyorganosiloxane copolymer-containing resin (this is one type of polycarbonate resin) and contains a fibril-forming polytetrafluoroethylene (Japanese Patent Laid-Open No. 81620/1996). Even though its polyorganosiloxane content is low, falling within a specifically defined range, the composition exhibits good flame retardancy. However, the composition is problematic in that its impact resistance characteristic of polycarbonate resin is often not good though its flame retardancy is good.
The second aspect of the invention has been made in consideration of the situation as above, and its object is to provide a polycarbonate resin composition of which the advantages are that its moldability, or that is, melt flowability is improved not detracting from the impact resistance thereof characteristic of polycarbonate resin, its flame retardancy, heat resistance and recyclability are all good, and it can be molded into thin-walled moldings that are lightweight and save natural resources, and to provide such moldings of the composition.
Of various thermoplastic resins, polycarbonate resins have a high oxidation index and are therefore self-extinguishable. In general, however, the flame retardancy level needed in the field of OA appliances and other electric and electronic appliances is high, concretely, V-0 as the UL94 Standard. For making those appliances resistant to flames to the desired level, therefore, flame retardant and flame retardation promoter are added thereto. However, the additives lower the impact resistance and the heat resistance of the appliances.
In particular, flame-retardant materials of good flowability are desired these days for large-sized and thin-walled moldings for housings of copiers and printers. The flowability of polycarbonate-polyorganosiloxane copolymers could be increased by reducing the molecular weight thereof according to the technology mentioned above, but this is problematic in that the impact resistance of the copolymers is low. On the other hand, the flowability of polycarbonate resins could also be increased by reducing the molecular weight thereof, but this is also problematic in that the flame retardancy and the impact resistance of the resins are low
The third aspect of the invention has been made in consideration of the situation as above, and its object is to provide a polycarbonate resin composition of good flowability, impact resistance and flame retardancy.